1. Field of the Invention
The present invention relates to a semiconductor structure, and further relates to applications of such a semiconductor structure.
2. Description of the Background Art
In RFID or remote sensor systems, use is frequently made today of passive backscatter transponders and remote sensors, which have no internal energy source, for example in the form of a battery, but instead extract the energy needed to power their integrated circuits (IC) from a high-frequency (HF) electromagnetic field radiated from a base station of the system. For this purpose, such transponders or remote sensors contain rectifier circuits which take energy that is transported by an HF carrier wave, captured by a suitable receiving device (antenna), and made available at what is called a (connecting) pad of the transponder or sensor IC, and convert the carrier wave into a DC supply voltage more suitable for operating the IC. Care must be taken in this process to ensure that the effects of parasitic circuit components such as resistors or capacitors—for short: parasitics—remain as small as possible, especially in the region of an input circuit, i.e. the pad of the transponder or sensor, since such components can otherwise have serious negative effects on the aforementioned systems on account of the dominant frequencies in the MHz or GHz range. Similar considerations also apply to the circuits for detecting the strength of a received signal (RSSI circuits) for use in the aforementioned systems.
A variety of different approaches exist for reducing the effects of parasitic circuit components. On the one hand, efforts are made to provide unavoidable parasitics with high quality factors to make it easier to compensate for them later. However, there also exists the possibility of providing parasitics with the lowest possible quality factor, so they no longer have an effect. This approach can only be poorly implemented, however, especially in ICs with small dimensions, since implementing large resistors with low quality factors results in a corresponding need for space that is not available in many IC architectures and is thus cost-intensive. Moreover, an obvious method is to attempt to permit only the smallest possible parasitics in the corresponding circuit components from the beginning through suitable designs.
It is known in this context that an input impedance with the smallest possible series resistance in the equivalent schematic is advantageous, since this results in a high quality factor for the input circuit. In addition, circular pad structures are generally used to keep the parasitic input capacitance at a low level. It is also known that the quality factor of a zone of semiconductor material located under the pad can be improved by a low dopant level.
In the German patent application 101 21 855.9, which corresponds to U.S. Publication No. 2002163976, which is incorporated herein by reference, relating to a Method for Matching an Antenna Tuned Circuit of a Passive Transponder, an approach is disclosed in relation to a semiconductor structure of the generic type according to which the quality factor of an input pad and thereby of a subsequent rectifier circuit can be improved by a lateral arrangement—relative to the electrically conductive layers—having a first zone of a first conductivity type and at least one highly doped second zone of a second conductivity type that is enclosed by the first zone.
Furthermore, there are known from the unpublished German patent application 103 22 888, which corresponds to U.S. Publication No. 2004245344, which is incorporated herein by reference, relating to an Integrated Circuit with Transponder, approaches to solutions for various rectifier circuits, by means of which parasitic effects can likewise be minimized through skillful selection and arrangement of Schottky diodes.